It is often necessary to mount a body to a channel member having a restricted mouth. Such channel members may be provided on the rear of a sign, the body to be mounted being a supporting post for the sign. Alternatively the channel member may be a structural element to which a body, such as an electric cable or group of cables are to be mounted. Frequently the channel members are of soft aluminium, whereas the mounting devices have to be of high tensile material such as stainless steel. Some signs, however, do not have such channel, but may have a return flange at the edge. It is an object of the present invention to provide a mounting device which is of wider applicability than the majority of mounting devices hitherto known.